Engineering student James McVay created a project for his fourth year at Victoria University of Wellington: MechBass, a robotic bass guitar. He designed everything in Solidworks and assemble lasercut/3D printed parts together. "The pitch shifter is open loop, with a NEMA23 stepper driving it to the desired position, and limit switches allowing alignment upon startup."

Pitch shifter carriage

McVay uses a customized control board which is based upon the ATMega328 (for Arduino compatibility) to control the plucking, fretting and damping of four strings, and each string only responds to MIDI messages on their designated MIDI channel.

Also the stepper motor for each pickwheel has a servo to enable the motor to be pivoted, bringing the picks closer to or further away from the string, allowing the volume of the picks to be altered. It has 3 power supply units (750 watts total) attached to modelar connectors.

A NEMA 17 pickwheel with servo velocity control

The constructed MechBass (images credit: James McVay)

McVay's design and implementation is uploaded here as a .pdf file. But first check out this video below MechBass playing Muse's "Hysteria".